Heat naturally moves from warmer places to cooler places. Heat pumps use electricity to move heat in the opposite direction, from cooler places to warmer places, making the cool space cooler and the warm space warmer. Your refrigerator is a heat pump, moving heat from inside the refrigerated cabinet (cooler place) into your kitchen (warmer place). An air conditioner is a heat pump, moving heat from inside your home (cooler place) to the outside summer air (warmer place).

Air-source heat pumps (ASHPs) are also used to heat homes, taking advantage of the fact that in the spring, fall - and yes, even in the winter - there is some heat in the outdoor air. Using a refrigerant, an ASHP absorbs heat from the outdoor air, concentrates it via an outdoor compressor, and distributes it inside through an indoor room unit or a home’s ductwork. During the summer, a heat pump can operate in reverse, as an air conditioner, by moving heat from indoors to the outside air.

Heat pumps require electricity to run, but can deliver more energy in the form of heat moved into a home than they use in electricity for operation. It takes far less energy to move heat than it does to create heat, as electric resistance or fossil fuel heating systems do. As a result, ASHPs are one of the most efficient home heating systems available.

Check out this video from Mass Save, the state's investor-owned utility energy efficiency program, for a visual explanation of how ductless mini-split heat pumps work (and read on to learn more about the types of heat pumps available!).

Ductless air-source heat pumps are exactly as they sound: heat pumps that don't require that you have ductwork in your home. Each ductless system includes one outdoor unit connected to one (single-zone) or more (multi-zone) indoor wall, floor or ceiling air distribution units. Ductless ASHPs are often referred to as ductless mini-splits (if one indoor unit is connected to each outdoor unit), or ductless multi-splits (if two or more indoor units are connected to each outdoor unit).

Ductless air-source heat pumps can be installed as a primary source of heating and cooling or installed to heat and cool specific rooms. This could include, for example, installing ductless units in the most frequently used rooms like family rooms or master bedrooms to displace heating or cooling from your existing system, or placing ductless units in rooms or new additions that never seem to be warm or cool enough.

These systems can be used for heating, cooling, dehumidification or as a fan. Because each indoor unit can be controlled individually, you can reduce your energy use even more by lowering the temperature in rooms that are not being used.

Ducted (also known as central or unitary) air-source heat pumps have an outdoor unit that is connected via refrigerant lines to an indoor air handler that uses a building's ductwork to distribute heating or air conditioning throughout the home. Note that not all ductwork is sized adequately for heat pumps, especially in older homes. Heat pump installers can tell you if your ductwork is sized adequately and what modifications may be necessary.

Regardless of whether a system is ductless or ducted, all ASHPs will have an outdoor unit (pictured below), which will be mounted on a ground platform or on the side of your home.

Above: A ductless ASHP outdoor unit; Below: A ducted ASHP outdoor unit.If you’re installing a ducted ASHP, the outdoor unit will be connected to a central air handler similar to one used by a furnace or central AC system. If you’re installing a ductless ASHP, the outdoor unit will typically be connected to one or more wall-mounted units (pictured below).

For homeowners that might not have suitable wall space or don’t like the aesthetic look of the wall-mounted indoor unit, floor-mounted (below) and ceiling-recessed units are also available, though these units cost more to install.

There are many reasons why an air-source heat pump could be a good fit for your home:

Improved home comfort. Advanced air-source heat pumps are "variable capacity," which means they can provide just the right amount of heating or cooling without temperature swings and constantly turning on and off. Also, they are quieter than most air conditioners and furnaces.

Energy savings. If you heat with oil, propane, or electric resistance (such as electric baseboards), you could save hundreds of dollars a year on your heating bill by installing an air-source heat pump. No need to pay thousands of dollars to get a natural gas connection to your home: a cleaner alternative is already available.

High-efficiency cooling, no ductwork required. Air-source heat pumps also provide air conditioning and dehumidification, and are more efficient than window air-conditioning units and most central air conditioning systems. Ductless ASHPs can allow you to reclaim your windows and avoid having to install ductwork to stay comfortable in the summer.

Improved health and air quality. In addition to providing cooling, heat pumps filter and dehumidify air, which can improve the air quality and comfort of your home. In particular, the filtration provided by advanced ASHP systems can significantly reduce allergens in your home for sensitive individuals.

Flexible options. Heat pumps are a flexible technology that can be installed in homes of all shapes and sizes with different needs - whether you need a whole-home system replacement, have (or don’t have) ductwork, want to add zoning to your home, want to increase the efficiency of heating part of your home, or want to add extra heating/cooling to that part of your home that’s never as comfortable as it should be.

Lower your carbon footprint. As a clean heating and cooling technology, converting from burning fossil fuels to using an air-source heat pump will reduce your carbon footprint and dependence on imported fossil fuels. Using solar PV or other renewable electricity sources can further offset emissions from the electricity powering your heat pump.

Traditional ASHPs are known for their poor cold-climate performance: these systems have been primarily used in the South for decades and are optimized for a warmer climate where air conditioning needs are higher.

There are now cutting-edge cold-climate models that are optimized for New England weather. These cold climate ASHPs are certified based on their performance at 5°F and many models can continue providing heat even when winter air is well below zero, down to -10°F or more.

Concerned about heat pump performance in January? Don't be. Mainers and Vermonters have installed more cold-climate heat pumps than any other New England state in the past few years—over 30,000 since 2013, and both states are significantly colder than Massachusetts in the winter!

While ASHPs are a great fit for many New England homes and businesses, they, like other heating and cooling systems, have potential drawbacks:

Performance in extreme cold. Because ASHPs rely on extracting heat from the outdoor air, the heating output and efficiency of ASHPs declines as outdoor air temperature declines. While cold climate ASHPs are rated based on their performance at 5°F, for many homes your installer will recommend keeping a backup system (your existing system or added electric resistance) for the coldest days of the year. In addition, if you’ve chosen to install ductless ASHPs to heat only specific rooms, another heating system will be required to heat the rest of the house.

Aesthetic considerations. ASHP outdoor unit and piping and ductless ASHP indoor equipment (e.g. wall-mounted units) may be aesthetically displeasing to some homeowners. That said, surveys suggest that most homeowners quickly become accustomed to the presence of indoor units. Your installer can discuss a variety of options available to you to minimize aesthetic impacts from an ASHP installation.

Manual coordination of thermostats. Thermostats for ductless ASHPs typically operate independently of your existing thermostat. This means that you will need to set your existing thermostat lower than your ASHP thermostat to ensure that your ASHP does the bulk of the heating. Some models can allow your heat pump system to control your backup system.

Higher installed costs. ASHPs generally cost more upfront than fossil fuel or central AC systems. However, their higher efficiency can pay back the difference over the course of several years.

Lower efficiency than ground-source heat pumps (GSHPs). Since the outdoor air is more variable in temperature than the ground, ASHPs are typically less efficient than GSHPs (aka, geothermal heat pumps). However, ASHPs are usually cheaper and quicker to install.

Air-source heat pumps are considered to be clean heating and cooling systems because they do not create heat, but rather they move existing heat in the outdoor air into your home. Further, this process is powered by electricity, which one can purchase or generate from carbon-free sources like solar, wind, or hydro. Electricity supplied by the Concord Municipal Light Plant was 54% carbon-free in 2018. That percentage will be even higher in 2019!

ASHPs are typically rated for heating efficiency based on their Heating Seasonal Performance Factor (HSPF) which describes the system’s efficiency over the course of the heating season. The seasonal efficiency of ASHPs can range from 220% to 300%+ depending on the system type, application, and seasonal weather patterns. That means that for every one unit of electricity used, 2.2 to 3 units of heat are transferred into the home. By comparison, electric resistance heating has an efficiency of 100%, and fossil fuel boilers and furnaces are typically 75- 82% efficient, with some models up to 95% efficient.

ASHPs also provide high-efficiency cooling—better than window AC units and comparable to the highest-efficiency central air conditioners.

Annual system maintenance, which consists of cleaning air filters and an annual maintenance checkup for the outside unit, costs about the same as annual servicing charges for a boiler or furnace. You can also clean the filters yourself, which can help to keep your system running well for many years (ask your installer for tips on how best to do this!).

Otherwise, the only other maintenance requirement would be to keep your outdoor unit clear of snow during the winter. (Installers often mount outdoor units on pedestals to reduce or eliminate this requirement.)

Most don't. There are water heaters that use heat pump technology, called heat pump water heaters (HPWHs). Ask your ASHP installer if they install HPWHs. HPWHs can also be installed by almost any plumber who installs water heaters.

Most installations are straightforward, with minimal disruption to your home. A simple, single-zone ductless ASHP system can be completed in less than a day and only requires a single 2-3 inch hole to be cut (and later, sealed) in your wall.

If you are installing a “multi-zone” ductless system or a ducted system that requires modifications to your ductwork, your installation may take a few days or more to complete.

“Set it and forget it.” While many of us are used to turning off the lights and turning down the heat when you leave the home or go to sleep, heat pumps are most efficient when running continuously at partial output without sudden increases in heating demand from cranking up the thermostat. Think about how your car’s mileage improves when you drive at a constant speed instead of constantly stopping and starting. Consider only setting back your heat pump system thermostat when you’re gone for several days.

Know when to use your backup system. Depending on the weather and the cost of your backup heating fuel, it may be best to use your backup system during the coldest parts of the year when heat pumps are at their least efficient. Learn more here about how to get the most out of your heat pump when used in conjunction with a back up system.

Keep your system well-maintained. A well-maintained system will keep performing at high efficiency. Remember to clean your indoor dust filters; keep the outdoor unit free of snow, ice, and other obstructions; and get an annual service check.

Weatherize your home. A heat pump in a well-insulated and well-sealed home will perform better than a poorly-weatherized home. Get a home energy assessment through Mass Save (natural gas heating households) or the Concord Municipal Light Plant (oil and electric heating households), and consider implementing the Energy Advisor’s insulation and air sealing recommendations prior to soliciting proposals for an ASHP installation. Not only will your home be even more comfortable and your system perform better, but it may allow you to install a smaller (and cheaper) ASHP to meet your home’s needs.

A properly-functioning heat pump may occasionally blow air that feels cooler than expected, particularly relative to a furnace. There are two reasons this may occur:

Heat pumps do not provide the same blast of very hot air that furnaces provide just due to the nature of how they generate heat: heat pumps are transferring heat from outdoors as opposed to heating air by burning fossil fuels. When it’s particularly cold outside, this air can feel cool to the touch but may still be 75-80°F or more and is working normally.

Heat pumps occasionally run in “defrost mode” to keep the outdoor unit clear of any frost buildup. For a few minutes your heat pump will stop producing heat, which can sometimes include a sudden, brief blast of cooler air. This is normal during winter operation and will not compromise the performance of your system.

If your heat pump is providing inadequate heat, you may consider using your backup system during temperature extremes. If your heat pump continues to blow cold air, you may have a maintenance issue with your system and should contact an installer.

According to the Massachusetts Clean Energy Center’s (MassCEC’s) ASHP Costs Comparison Tool, the median cost in Middlesex County is $3,700 per ton of heating capacity at 5°F for a single-head (i.e. single-zone) unit and $4,600 per ton for a multi-head unit. Note that as of early 2019, the cost data does not include over 150 ASHPs that had been installed in Concord and had received rebates from the Concord Municipal Light Plant rather than from MassCEC. That number continues to grow. In 2018, residential ASHP installations in Concord averaged 3 tons of heating capacity at 5°F.

At 2018 heating oil, propane and electricity prices, the cost savings from using heat pumps pay for the additional upfront cost more quickly in some circumstances than in others. The payback period depends on whether a home currently has central AC, and if so, whether a home’s heating system and/or central AC are at end of life and need to be replaced. See the summary table below for ranges of typical payback periods.

At 2018 prices, natural gas-heating households won’t cut costs by using air-source heat pumps. Therefore, there are no cost savings to offset the additional upfront cost of replacing natural gas-fired heating equipment with heat pumps rather than with conventional equipment.

The economics of investing in heat pumps will vary based on your specific circumstances, and payback periods may or may not fall within the estimated ranges listed above. Many people invest in heat pumps for quality of life benefits as well as cost savings. These may include adding AC to your home, replacing inconvenient window AC units, or having more control over temperature in individual rooms. Others also invest in heat pumps to reduce their carbon footprint.

Many HVAC (Heating, Ventilation and Air Conditioning) contractors install ASHPs. If you have a good HVAC contractor who has installed heating or air-conditioning equipment for you in the past, ask them if they have experience installing ASHPs.

We suggest soliciting proposals from at least three heat pump installers. Seek proposals from HVAC contractors who can provide a letter or certificate from the manufacturer verifying that their installation technicians have successfully completed at least 4 hours of manufacturer training within the last 5 years for the type of products (i.e. ductless or ducted) that they install. The manufacturer training need not have been provided by the manufacturer of the same equipment brand that is being installed in your home, but it should be provided by a manufacturer of the same equipment type (i.e. ductless training if ductless equipment is installed; ducted training if ducted equipment is installed.)

We recommend that you request the installer submit this documentation to you with their proposal. The documentation will be required if you wish to apply for a rebate from the Concord Municipal Light Plant for your heat pump.

The following HVAC contractors have installed heat pump systems for Concord residents who have received air-source heat pump rebates from the Concord Municipal Light Plant. CMLP does not endorse, nor have we pre-qualified these companies in any way. CMLP accepts no liability for work conducted by any contractor. You do not need to use an installer on this list to receive a rebate from CMLP.

The Massachusetts Clean Energy Center also maintains a list of air-source heat pump installers that participate in their air-source heat pump rebate program, which is available to electricity customers in communities served by Eversource and National Grid.

Keep in mind that for any type of home heating or cooling system to work well, it must be selected, sized, and installed properly. The low-cost installer may not be your best option. Further, if your installer is not already aware of it, refer them to the best practice guidance related to sizing, selecting and installing ASHPs in cold climates, as described in the Northeast Energy Efficiency Partnership’s (NEEP’s) installer guides.

Is the specific system(s) you are proposing listed on NEEP’s (Northeast Energy Efficiency Partnership’s) Cold Climate Air-source Heat Pump (ccASHP) Specification Product Listing (available here)? If not, what is the rationale for choosing a system that is not listed?

Where will you install the outdoor unit(s), and why?

Will you elevate the outdoor unit(s)?

Where will you install the indoor unit(s), and why?

If the equipment is intended to serve as my home’s only source of heat: Have you determined my home’s heating and cooling design loads using ACCA Manual J, and sized the equipment accordingly?

Experience and Training

Can you provide references from previous customers with similar systems?

Can you provide a letter or certificate verifying that your installation staff has participated in at least 4 hours of manufacturer training in the last 5 years for the type of systems you would install in my home? The manufacturer training need not have been provided by the manufacturer of the same equipment brand that is being installed in my home, but it should be provided by a manufacturer of the same equipment type (i.e. ductless training if ductless equipment is installed; ducted training if ducted equipment is installed.)

If your ASHP is your only heating source, you are eligible to receive and sell Alternative Energy Certificates (AECs), which are awarded to owners of clean heating & cooling technologies through the Commonwealth's Alternative Portfolio Standard. The number of certificates you receive will be based on a variety of criteria, including the size and efficiency of your home (e.g. if your home has a HERS rating of <50 or is a "Zero Energy" Home or Passive House).

Depending on these factors—and the value of the AECs at quarterly auctions, you could receive $1,200-$4,500 for a whole-home ASHP system.

An Excel calculator developed by the Dept. of Energy Resources is available here. Please note that a default AEC value of $20/MWh is assumed in this calculator. We would recommend using a more conservative estimate of $15/MWh or lower to represent a lower auction value of these AECs and an aggregator fee of ~7% or more.

Speak with your installer to learn more about the APS and the incentive you could receive for your system.